The processing of a component that will be later subjected to stresses in service has a significant effect on the service life of the component. A major factor determining the service life of a component is surface integrity, which may be defined as the result of alterations produced in a surface layer during manufacture of a component and which affect the material properties and performance of the component in service. Typically, three factors are considered for surface integrity: surface finish, microstructure and residual stress. The prior art has long given considerable attention to a component's surface finish and physical and material properties in order to meet design requirements such as strength, fatigue and wear, with finish grinding, honing, lapping, polishing, electropolishing and abrasive superfinishing techniques used to achieve various levels of surface finish. However, because the shape and orientation of the abrasive particles used in finish grinding and other finishing techniques cannot be controlled, material removal by such techniques cannot be controlled in a manner that will predictably and controllably remove residual tensile stresses induced in the surface by the manufacturing operation used to form the surface, such as turning, milling, etc. Consequently, the prior art has conventionally relied on peening with glass or steel shot to create a compressive layer in a component surface to compensate for machining damage and detrimental residual tensile stresses that were imparted during the manufacture of the component. Shot peening has also been employed to suppress crack growth associated with surface and near-surface inclusions in machined powder metal components. Accordingly, shot peening of the surfaces of machined components is widely employed to improve the service life of such components.
However, the service life of the component can be reduced as a result of cold working caused by high intensity and high coverage peening employed to overcome significant levels of residual stresses in a component surface. To reduce the negative effects of surface cold working, attempts have been made to reduce the intensity and coverage of the operation, and to use different shot size and material. Such attempts have had a negative impact on service life and/or manufacturing costs.
Therefore, it would be desirable if a method were available for improving the service life of a component by improving the surface integrity of a component, while overcoming the shortcomings of conventional shot peening techniques.